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Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (anc)

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Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (anc)


A personal audio device, such as a wireless telephone, includes noise canceling that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone is provided proximate the speaker to measure the output of the transducer in order to control the adaptation of the anti-noise signal and to estimate an electro-acoustical path from the noise canceling circuit through the transducer. The anti-noise signal is adaptively generated to minimize the ambient audio sounds at the error microphone. A processing circuit that performs the adaptive noise canceling (ANC) function also filters one or both of the reference and/or error microphone signals, to bias the adaptation of the adaptive filter in one or more frequency regions to alter a degree of the minimization of the ambient audio sounds at the error microphone.

Inventors: Nitin Kwatra, Ali Abdollahzadeh Milani, Jeffrey Alderson
USPTO Applicaton #: #20120308028 - Class: 381 7111 (USPTO) - 12/06/12 - Class 381 
Electrical Audio Signal Processing Systems And Devices > Acoustical Noise Or Sound Cancellation >Counterwave Generation Control Path >Adaptive Filter Topology

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The Patent Description & Claims data below is from USPTO Patent Application 20120308028, Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (anc).

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This U.S. Patent Application Claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/493,162 filed on Jun. 3, 2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to personal audio devices such as wireless telephones that include noise cancellation, and more specifically, to a personal audio device in which the anti-noise signal is biased by filtering one or more of the adaptation inputs.

2. Background of the Invention

Wireless telephones, such as mobile/cellular telephones, cordless telephones, and other consumer audio devices, such as MP3 players and headphones or earbuds, are in widespread use. Performance of such devices with respect to intelligibility can be improved by providing noise canceling using a microphone to measure ambient acoustic events and then using signal processing to insert an anti-noise signal into the output of the device to cancel the ambient acoustic events.

The anti-noise signal can be generated using an adaptive filter that takes into account changes in the acoustic environment. However, adaptive noise canceling may cause an increase in apparent noise at certain frequencies due to the adaptive filter acting to decrease the amplitude of noise or other acoustic events at other frequencies, which may result in undesired behavior in a personal audio device.

Therefore, it would be desirable to provide a personal audio device, including a wireless telephone, that provides noise cancellation in a variable acoustic environment that can avoid problems associated with increasing apparent noise in some frequency bands while reducing apparent noise in others.

SUMMARY

OF THE INVENTION

The above stated objective of providing a personal audio device providing noise cancellation in a variable acoustic environment, is accomplished in a personal audio device, a method of operation, and an integrated circuit. The method is a method of operation of the personal audio device and the integrated circuit, which can be incorporated within the personal audio device.

The personal audio device includes a housing, with a transducer mounted on the housing for reproducing an audio signal that includes both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer. A reference microphone is mounted on the housing to provide a reference microphone signal indicative of the ambient audio sounds. The personal audio device further includes an adaptive noise-canceling (ANC) processing circuit within the housing for adaptively generating an anti-noise signal from the reference microphone signal. An error microphone is included for controlling the adaptation of the anti-noise signal to cancel the ambient audio sounds and for correcting for the electro-acoustic path from the output of the processing circuit through the transducer. The anti-noise signal is generated such that the ambient audio sounds are minimized at the error microphone. One or both of the reference microphone and/or error microphone signals are filtered to weight one or more frequency regions in order to alter a degree of the minimization of the ambient audio sounds in the one or more frequency regions.

The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a wireless telephone 10 in accordance with an embodiment of the present invention.

FIG. 2 is a block diagram of circuits within wireless telephone 10 in accordance with an embodiment of the present invention.

FIG. 3 is a block diagram depicting signal processing circuits and functional blocks within ANC circuit 30 of CODEC integrated circuit 20 of FIG. 2 in accordance with an embodiment of the present invention.

FIG. 4 is a block diagram depicting signal processing circuits and functional blocks within an integrated circuit in accordance with an embodiment of the present invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENT

The present invention encompasses noise canceling techniques and circuits that can be implemented in a personal audio device, such as a wireless telephone. The personal audio device includes an adaptive noise canceling (ANC) circuit that measures the ambient acoustic environment and generates an adaptive anti-noise signal that is injected in the speaker (or other transducer) output to cancel ambient acoustic events. A reference microphone is provided to measure the ambient acoustic environment and an error microphone is included to control adaptation of the anti-noise signal to cancel the ambient acoustic events and to provide estimation of an electro-acoustical path from the output of the ANC circuit through the speaker. An adaptive filter minimizes the ambient acoustic events at the error microphone signal by generating the anti-noise signal from the reference microphone signal using an adaptive filter. The coefficient control inputs of the adaptive filter are provided by the reference microphone signal and the error microphone signal. The ANC processing circuit avoids boosting particular frequencies of the reference microphone signal, thereby increasing noise at those frequencies, by filtering one or both of the reference microphone and error microphone signal provided to the coefficient control inputs of the adaptive filter, in order to alter the minimization of the ambient acoustic events at the error microphone signal. By altering the minimization, boosting of the particular frequencies can be prevented.

Referring now to FIG. 1, a wireless telephone 10 is illustrated in accordance with an embodiment of the present invention is shown in proximity to a human ear 5. Illustrated wireless telephone 10 is an example of a device in which techniques in accordance with embodiments of the invention may be employed, but it is understood that not all of the elements or configurations embodied in illustrated wireless telephone 10, or in the circuits depicted in subsequent illustrations, are required in order to practice the invention recited in the Claims. Wireless telephone 10 includes a transducer such as speaker SPKR that reproduces distant speech received by wireless telephone 10, along with other local audio event such as ringtones, stored audio program material, injection of near-end speech (i.e., the speech of the user of wireless telephone 10) to provide a balanced conversational perception, and other audio that requires reproduction by wireless telephone 10, such as sources from web-pages or other network communications received by wireless telephone 10 and audio indications such as battery low and other system event notifications. A near-speech microphone NS is provided to capture near-end speech, which is transmitted from wireless telephone 10 to the other conversation participant(s).



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Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (anc)
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Continuous adaptation of secondary path adaptive response in noise-canceling personal audio devices
Industry Class:
Electrical audio signal processing systems and devices
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stats Patent Info
Application #
US 20120308028 A1
Publish Date
12/06/2012
Document #
13472755
File Date
05/16/2012
USPTO Class
381 7111
Other USPTO Classes
International Class
10K11/16
Drawings
5



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